Dry cat food works fine, but... cats are carnivores. Not omnivores. Usually if they're eating actual vegetation, they're sick, same as dogs. Have no idea if some kind of processed vegetable diet can function well for them, but I'd be somewhat surprised if it were possible. You might be able to buy live mice or rats ala snake feeding if you don't want to support the primary livestock industry, though. Probably be a bit messy and I have no idea what kind of feeding intervals that'd take. It'd be pretty bloody expensive, though. E: Missed the verification bit, sorry. Only backup I can provide is anecdotal, but I've had cats fairly consistently for a couple of decades now. Ask the vet when you take 'em in, they can give you a more qualified opinion.
As for neutering, it can change things up a bit with behavior, but if you don't do it, you can expect a litter every year or so, per cat (unless you very carefully keep them inside), which... adds up. Quickly. Especially if you don't already have a good idea of what to do with the excess. You don't have the space or resources to keep up with cat output, especially if something isn't killing off parts of the litters. No, I don't know your particular situation, but it's fairly irrelevant. DF catsplosion is only somewhat exaggerated.
As for indoor/outdoor... there's, uh, not really a kind of breed specification re: that, so far as I know. If you keep them indoor, they're a bit less likely to disappear some day, but that entails some extra effort (litter box(es), oi.). It's a matter of preference and cat personality.
Collar can serve two primary purposes beyond decoration -- they can hold a tag with owner information and they can be a flea collar. Flea collar tends to be a bit less effective than specialized medication, but it helps. As for toys, ehn. They don't need them, per se, but they don't hurt. You can improvise cat toys pretty easily (Feather on a stick? Feather on a stick. Ponytail? Ponytail. So on, so forth.).